San Antonio · AC Relay Repair · Family-Owned Since 1996
If your AC starts and stops randomly, doesn't respond to the thermostat, or only kicks on sometimes, a failed relay on the control board is almost always the culprit. Most relay jobs done in under an hour.
Typical price
$180–$320 installed
Time to fix
30–90 minutes
Urgency
Medium — system is unpredictable
A relay is a small electromechanical switch — basically a tiny version of a contactor — used inside your furnace or air handler control board, fan center, or as a standalone component to control things like the blower, condenser, or accessories like a UV light or dehumidifier.
Relays fail when their contacts pit and burn from repeated switching, exactly like contactors do. The difference is they're smaller, switch lower current, and live indoors — so they last longer (8-12 years typical), but they're still wear items.
When a relay fails, the symptoms are usually intermittent and frustrating: the AC starts and stops, runs at the wrong times, or won't respond to the thermostat at all. Because there can be 3-6 relays in a typical residential system, isolating which one is bad takes a proper diagnosis.
What it costs in San Antonio
$180–$320 installed — Standalone relays on the lower end. Control board relays where the whole board has to be replaced: $350–$650. Our $59 diagnostic is waived when you approve the repair, so you only pay for the fix itself.
If two or more of these sound familiar, it's probably your ac relay.
Here's exactly what a Carnes and Sons tech does at your house — no mystery, no upselling.
Intermittent problems require us to actually see the failure. We let the system run a normal cool cycle while watching the control board with a meter — we can spot a relay that's chattering, sticking, or failing to make contact.
Across the relay coil we measure 24V control voltage. Across the contacts (when energized) we measure less than 0.5 ohms. Anything else means the relay is failing.
Some relays are socketed (plug-in) — we can swap just the relay for $180-$280. Others are soldered to the control board — at that point it's usually smarter to replace the whole board for $350-$650 than to try to repair the board.
We match coil voltage (usually 24VAC) and contact rating exactly. We carry common Honeywell, White-Rodgers, and Mars relays on every truck.
Once installed we cycle the system multiple times — start, stop, fan-only, auto — to make sure the new relay seats and switches cleanly. We don't leave on a 'works once' test.
Get Your AC Relay Diagnosed Today
Tell us what's happening. We'll text you back in minutes — no call center, no robo-calls.
$180 to $320 installed for a standalone relay. If the bad relay is soldered into a control board, the typical fix is to replace the whole board for $350 to $650. We'll tell you which one applies before quoting.
Same idea, different scale. A contactor is the heavy-duty relay outside that switches high-voltage to your compressor and condenser fan. Indoor relays are smaller, switch lower current, and control things like the blower motor, accessories, and zone dampers.
Usually one of three things: (1) a relay that's making intermittent contact, (2) a failing thermostat, or (3) a low-voltage wiring issue. A proper diagnosis isolates which — we won't just throw a thermostat at it and hope.
Short-term yes, but every breaker trip risks damaging the compressor (the most expensive part in your system). If you're flipping the breaker more than once a week, something is wrong — get it diagnosed before it costs you a $2,500 compressor.
8 to 12 years in San Antonio. Heat shortens lifespan, surge protection extends it. If you've had 2 relays fail on the same system in a year, there's an underlying problem (usually a stuck contactor or a wiring fault) that needs to be found.
Yes. A whole-house surge protector at the panel and a dedicated HVAC surge protector at the air handler/condenser ($200-400 installed) prevent the majority of CPS Energy-induced relay and board failures we see in summer.
Not strictly — your system is running, just unpredictably. But because the failure pattern often gets worse fast (intermittent becomes constant), and because running with a faulty relay can damage the compressor, we treat it as a same-day call.
1 to 5 years parts depending on the brand, plus 1 year labor.
We're based in Stone Oak and roll trucks across San Antonio and the surrounding Hill Country every day.
License TACLB29435E · Family-Owned Since 1996
Cities & neighborhoods we serve
San Antonio · Stone Oak · Alamo Heights · Hollywood Park · Hill Country Village · Shavano Park · Castle Hills · Leon Valley · Helotes · Boerne · Fair Oaks Ranch · Bulverde · Timberwood Park · Garden Ridge · Schertz · Cibolo · Selma · Universal City · Live Oak · Converse · Windcrest · New Braunfels
No call center. The owner or one of his sons picks up.
(210) 600-5091